Pain tolerance in opioid addicts on and off naltrexone pharmacotherapy: a pilot study

Evolution of Analgesic Tolerance and Opioid-Induced Hyperalgesia Over 6 Months: Double-Blind Randomized Trial Incorporating Experimental Pain Models

Contributors to the ongoing epidemic of prescription opioid abuse, addiction, and death include opioid tolerance, withdrawal symptoms, and possibly opioid-induced hyperalgesia (OIH). Thirty stable chronic nonmalignant pain patients entered a 6-month long, randomized, double-blind, dose-response, 2-center trial of the potent opioid levorphanol, conducted over a decade ago during an era of permissive opioid prescribing. Eleven were taking no opioids at study entry and eleven were taking between 35 and 122 morphine equivalents. Five weeks titration preceded twenty weeks stable dosing. Tolerance and OIH were inferred individually based on chronic pain ratings, brief pain inventory scores, and results of the brief thermal sensitization model at 5 opioid dosing sessions. Seventeen patients completed. The average final daily opioid dose was 132; range 14 to 300; average addition 105 morphine equivalents. After observed dosing, the brief thermal sensitization area of hyperalgesia changed minimally but the painfulness of skin heating was reduced. Weekly 0 to 100 visual analog scale pain ratings (average 64 at study entry, 48 at end titration, 45 at end stable dosing) decreased a median 19%, but 8 completed with higher visual analog scale ratings. Three completers had evidence of both tolerance and hyperalgesia. A fully-powered trial similar to this feasibility study is ethically questionable. A large-scale pragmatic trial is more realistic. TRIAL REGISTRATION: NCT00275249 Evolution of Analgesic Tolerance With Opioids PERSPECTIVE: A double-blind, 6-month, high-dose opioid feasibility trial, completed years ago, provides critically important data for clinically defining analgesic tolerance and OIH. Overall benefit was small, and 18% of patients had evidence of both tolerance and OIH. Future work requires a different approach than a classic randomized controlled trial design.

Medical and psychological risks and consequences of long-term opioid therapy in women

BACKGROUND

Long-term opioid use has increased substantially over the past decade for U.S. women. Women are more likely than men to have a chronic pain condition, to be treated with opioids, and may receive higher doses. Prescribing trends persist despite limited evidence to support the long-term benefit of this pain treatment approach.

PURPOSE

To review the medical and psychological risks and consequences of long-term opioid therapy in women.

METHOD

Scientific literature containing relevant keywords and content were reviewed.

RESULTS AND CONCLUSIONS

Long-term opioid use exposes women to unique risks, including endocrinopathy, reduced fertility, neonatal risks, as well as greater risk for polypharmacy, cardiac risks, poisoning and unintentional overdose, among other risks. Risks for women appear to vary by age and psychosocial factors may be bidirectionally related to opioid use. Gaps in understanding and priorities for future research are highlighted.

Randomized double-blind placebo controlled crossover study of acetaminophen, ibuprofen, acetaminophen/hydrocodone, and placebo for the relief of pain from a standard painful stimulus

OBJECTIVES

The objective was to compare subjects' change in perceived acute pain from an identical painful stimulus after receiving three separate, commonly used pain medications and placebo.

METHODS

This was an institutional review board-approved, randomized, double-blind crossover study of healthy human volunteers. Subjects received 1000 mg of acetaminophen, 800 mg of ibuprofen, the combination of 650 mg of acetaminophen with 10 mg of hydrocodone, or placebo (800 mg of lactose) in a randomized order over four separate occasions each 1 week apart. Prior to receiving the drug on each study day, subjects placed their nondominant hand in a bath of 0 degrees C water for 45 seconds. The bath was divided into two sections; the larger was the reservoir of cooled water monitored at 0 degrees C, and the other half was filled from constant overflow. Water drained from the overflow section into the cooling unit and was then pumped up into the base of the reservoir through a diffusion grid. Subjects completed a 100-mm visual analog scale (VAS) representing perceived pain during the exposure. The cold water exposure and VAS were repeated 1 hour after receiving the study drug, and then subjects were observed for side effects for 4 hours. Data were compared using descriptive statistics, 95% confidence intervals (CIs), and repeated-measures analysis of variance (ANOVA).

RESULTS

Twenty-five subjects were enrolled. The mean VAS preexposure was 56.9 mm (+/-15.1 mm; range = 5 to 92 mm). The mean decrease in VAS after receiving the study drug for acetaminophen was 10.2% (95% CI = -1.4 to 20.4), for ibuprofen was -6.6% (95% CI = -16.5 to 3.20), for acetaminophen/hydrocodone was 9.5% (95% CI = 1.4 to 20.4), and for placebo was -6.9% (95% CI = -15.2 to 1.4). The range in change in pain scores for all agents was -91.3% to 57.6%. Mild side effects (nausea, dizziness, or somnolence) were reported in 11 subjects (44%) after receiving acetaminophen/hydrocodone; no other side effects were reported.

CONCLUSIONS

There was a wide range of changes in pain scores from this identical painful stimulus after receiving the study medications. Acetaminophen and acetaminophen/hydrocodone resulted in a similar decrease in pain (10.2 and 9.5%), while ibuprofen and placebo had a similar lack of effect (-6.6 and -6.9%). Forty-four percent of subjects receiving acetaminophen/hydrocodone reported mild side effects; no other side effects were seen. In this noninflammatory pain model, the VAS is not able to distinguish differences in pain relief between acetaminophen and acetaminophen/hydrocodone or ibuprofen and placebo.

Understanding addiction: the orthopedic surgical perspective to a significant problem

The realm of addiction and addiction medicine is one in which physicians receive little formal training, particularly in surgical subspecialties. This article presents an overview of addiction medicine and treatment, concentrating on the neurophysiology, psychological aspects, and terminology. Assessment tools and objective findings for recognizing addiction in patients in pain are discussed, as is the management of acute pain and perioperative considerations for patients who are undergoing opioid treatment programs.

Substance use histories in patients seeking treatment for controlled-release oxycodone dependence

The characteristics of patients currently abusing controlled-release (CR) oxycodone admitted for inpatient detoxification were ascertained from medical record review of 48 inpatients with CR oxycodone dependence. Patients were categorized according to the manner in which they initially received the drug: illicitly or by prescription for legitimate medical use. Fifteen of the 48 patients (31%) initially obtained a CR oxycodone prescription legitimately for a medical condition. While none of these 15 patients had a history of prior opioid misuse, they were more likely than illicit CR oxycodone users to report prior detoxifications (P<0.03) as well as a lower mean age of first alcohol use (legitimate=11.7 versus illicit=14.7, P<0.05) and first illicit drug use (legitimate=12.8 versus illicit=15.8, P<0.05). These findings suggest that a history of substance abuse is common among patients abusing CR oxycodone, including individuals for whom CR oxycodone was initially legitimately prescribed for pain.

Chronic very low dose naltrexone administration attenuates opioid withdrawal expression

BACKGROUND

Different regimens of agonist and antagonist drugs have been used in opioid withdrawal management, with variable results. We examined whether administering extremely small quantities of opiate antagonists in the presence of opiate agonist drugs reduces withdrawal expression.

METHODS

Forty-one male Sprague-Dawley rats were implanted with morphine or placebo pellets for eight days. Starting on day 3, some rats received naltrexone in their drinking water (5 mg/L), or unadulterated water. On day 8, rats were injected with saline or naltrexone (100 mg/kg) and evaluated for behavioral signs of withdrawal. Next, sections through the locus coeruleus (LC) and nucleus of the solitary tract (NTS), brainstem areas exhibiting cellular activation following opiate withdrawal, were processed for c-Fos to detect early gene expression. Finally, the same nuclei were examined for protein kinase A regulatory subunit II (PKA) and phosphorylated cyclic adenosine monophosphate response element binding protein (pCREB), using Western blot analysis.

RESULTS

Withdrawal was attenuated and c-Fos, PKA, and pCREB expression was decreased in the NTS and LC of rats receiving chronic very low doses of naltrexone.

CONCLUSIONS

Reduction of withdrawal upon chronic very low naltrexone administration may be due in part to decreased activation of brainstem noradrenergic neurons in morphine dependent rats.

Temperature and the cold pressor test

As a method of experimental pain induction, the cold pressor test is thought to mimic the effects of chronic conditions effectively. A survey of previous studies using the cold pressor, however, revealed a lack of standardization and control of water temperature, questioning comparability and reliability. This study reports the influence of temperature on pain tolerance and intensity by using a commercially available circulating water bath. Twenty-six participants (12 men, 14 women) underwent 4 cold pressor trials with temperature order counterbalanced across 1 degrees C, 3 degrees C, 5 degrees C, and 7 degrees C, temperatures representative of the range used in previous literature. After each cold immersion participants rated pain intensity on a visual analogue scale and the McGill Pain Questionnaire. Tolerance times were recorded for each trial. Significant main effects of temperature were found for tolerance time, with higher temperatures resulting in longer times, and pain intensity, with lower temperatures resulting in higher intensities. Gender differences were found, with men tolerating the stimulus for significantly longer than women. It was concluded that small differences in water temperature have a significant effect on pain intensity and tolerance time. The use of cold pressor equipment that ensures a precise constant temperature of circulating water is necessary to ensure comparable and reliable results.

PERSPECTIVE

The cold pressor method of experimental pain induction has been widely used in the evaluation of psychological and physiological pain treatments. This article highlights the need for clear methodologic guidelines for the technique and demonstrates that very minor changes in experimental protocol can produce significant differences.

Intraoperative high-dose remifentanil in a patient on naltrexone therapy

Naltrexone hydrochloride is a synthetic opioid receptor antagonist recently used in efforts to provide rapid opioid detoxification. Other clinical uses include alleviating itch due to cholestasis or uraemia. We report a case where unrecognised naltrexone therapy for itch affected anaesthesia, resulting in high opioid requirements. We also discuss other analgesic options utilized.

Endogenous opiates: 1998

This paper is the twenty-first installment of our annual review of research concerning the opiate system. It summarizes papers published during 1998 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.